EGU2020-7501
https://doi.org/10.5194/egusphere-egu2020-7501
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Geological controls on the morphology of an overdeepened canyon investigated by seismic surface waves (Lower Aare Valley, Switzerland)

Lukas Gegg1, Lorenz Keller2, Marius W. Buechi1, Thomas Spillmann3, Gaudenz Deplazes3, Herfried Madritsch3, and Flavio S. Anselmetti1
Lukas Gegg et al.
  • 1Quaternary Geology and Paleoclimatology, Institute of Geological Sciences, University of Bern, Switzerland (lukas.gegg@geo.unibe.ch)
  • 2roXplore GmbH, Amlikon-Bissegg, Switzerland
  • 3National Cooperative for the Disposal of Radioactive Waste (Nagra), Wettingen, Switzerland

Subglacial overdeepenings are common features of past and presently glaciated landscapes. In the Northern Alpine Foreland, these troughs occur mostly within the rather soft, poorly lithified sandstones of the Molasse basin. An exceptional setting is the Lower Aare Valley in Northern Switzerland, where a narrow, finger-like overdeepening (Gebenstorf-Stilli Trough) has been incised more than 100 m below the present surface into the fold-and-thrust belt of the Jura Mountains with its diverse Mesozoic lithologies including competent limestone units. Consequently, the morphology of this overdeepening can provide valuable information on lithological and structural controls on subglacial overdeepening erosion.

We investigate the Gebenstorf-Stilli Trough with three scientific boreholes located along the South-North oriented trough axis. In addition, a set of seismic cross-sections has been acquired by a combination of active and passive seismic approaches analysing surface waves, namely passive horizontal-to-vertical spectral ratio (HVSR) measurements, active measurements applying multiple filter analysis of group velocity (MFA), and extended spatial auto correlation of ambient vibration array data (ESAC).

Preliminary results show that the base of the overdeepening can be well imaged using our methodology. In combination with borehole information, surface elevation data and 3D models of the subsurface geology, we see great potential to better constrain the morphology of the Gebenstorf-Stilli Trough, and to assess how different bedrock lithologies and structures influence subglacial overdeepening erosion – an underexplored and poorly understood issue.

How to cite: Gegg, L., Keller, L., Buechi, M. W., Spillmann, T., Deplazes, G., Madritsch, H., and Anselmetti, F. S.: Geological controls on the morphology of an overdeepened canyon investigated by seismic surface waves (Lower Aare Valley, Switzerland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7501, https://doi.org/10.5194/egusphere-egu2020-7501, 2020

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